Experimental study on bond performance between shotcrete and rock in a hot and humid tunnel environment

To study the bond performance between shotcrete and rock in a hot and humid tunnel, experiments on wet-sprayed shotcrete specimens under different hot and humid curing conditions (35A degrees C, 50A degrees C, 70A degrees C, and standard curing conditions: 20A degrees C with relative humidity 95%) were performed to examine the influence of thermal damage. The results show that the bond strength at 35A degrees C is higher compared with that at standard curing conditions, but decreases when the temperature rises (especially at 70A degrees C), indicating the adverse effects of thermal damage on bond strength. Based on these results, we used the worst hot and humid condition (70A degrees C) as a case study to explore measures to improve bond strength under hot and humid conditions by adding mineral admixture or fiber material to the shotcrete mix. The experimental results suggest that adding fly ash or slag powder can enhance the bond strength, with the best effect achieved by adding fly ash.